## July 12, 2005

### If It’s Tuesday, This Must Be Toronto

Toronto is undergoing what the locals consider a heat wave. While the absolute temperatures may not exceed those in Austin, it’s a lot more humid here, and air conditioning is less ubiquitous/effective.

Continuing my random, unsystematic and thoroughly idiosyncratic reportage…

Renata Kallosh talked about flux stabilization on $K3\times K3$. In the presence of fluxes, there are Euclidean D3 instanton (in M-theory, M5 instanton) corrections to the superpotential from divisors of arithmetic genus $\chi_{\mathcal{O}}=2$. In the absense of fluxes, only $\chi_{\mathcal{O}}=1$ contribute instanton corrections (though, in general, positive $\chi_{\mathcal{O}}$ can make “fractional instanton”, AKA gaugino condensate, contributions to the superpotential).

In the presence of flux, some of the zero modes are lifted, and higher values of $\chi_{\mathcal{O}}$ contribute instanton corrections. Aspinwall and Kallosh used this to fix all the moduli in compactification of M-Theory on $K3\times K3$ (where the relevant divisors, of the form $\mathbb{P}^1\times K3$ and $K3\times\mathbb{P}^1$, have $\chi_{\mathcal{O}}=2$).

Tomasiello gave a beautiful talk on his work with Graña et al on generalized complex geometry and N=1 supersymmetry in Type II compactifications with flux. I’ve meant to blog about Gualtieri and Hitchin’s work on Generalized Complex Structures for a while now. Maybe I’ll get around to it someday.

The afternoon was rather phenomenological, with a talk by Witten on axions in string theory and a talk by Arkani-Hamed on LHC physics. The “surprise” of Witten’s talk was that, really, there was no surprise. The axion decay constant, $f_a$, in the “new” string theory backgrounds is really not much different from that in the string backgrounds we knew about 20 years ago. With the notable exception of heterotic backgrounds with anomalous $U(1)$s, the typical value of $f_a\sim 10^{16}$ GeV. This has always been somewhat in conflict with purported cosmological upper bound, $f_a \lesssim 10^{12}$ GeV (which comes from demanding that axions not dominate the energy density)1. On the other hand, as noted by Banks et al, this cosmological upper bound is easily evaded.

Arkani-Hamed’s talk was a bit more upbeat. The prospects for extracting physics at the LHC are quite exciting. He discussed both “natural” theories (low-energy supersymmetry, little Higgs models, …) and “unnatural” ones (split supersymmetry), and what sort of signatures one could expect. The map, alas, from parameter space, in low-energy supersymmetry, to “signature space” is many-to-one. Sorting this out is the subject of the LHC Olympics.

No, I’m not going to talk about the panel discussion, except to mention Joe Polchinski’s quip about “Anthropic/CFT Duality.”

1 The lower bound, $f_a \gtrsim 10^9$ GeV, coming from supernovæ, seems solid.

Posted by distler at July 12, 2005 10:05 AM

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### Panel discussion

Hi,
it’s a pity that you don’t comment on the panel discussion.
Being a phd student I feel quite depressed after having listened to it.

Posted by: Florian Gmeiner on July 12, 2005 9:05 PM | Permalink | Reply to this

### Re: Panel discussion

Being a phd student I feel quite depressed after having listened to it.

My best suggestion is to ignore such silly exercises and get on with the business of doing physics.

Posted by: Jacques Distler on July 12, 2005 9:55 PM | Permalink | PGP Sig | Reply to this

### Re: Panel discussion

I too am a phd student (starting second year), interested in high energy theory, and am puzzled by your advice to “ignore such silly exercises and get on with the business of doing physics.” I didn’t attend the conference, but have the impression that the panel discussion was relevant to making an informed decision about risks of studying string theory. If that is correct, wouldn’t it be better to lay the cards on the table and discuss it openly so that students have the best available information to make an intelligent decision about their future? To be silent about possible big problems or act as though they don’t exist in the interest of “just doing physics” seems more appropriate to participation in a belief system than doing good science. There seems to be a lot of poorly informed opinion on the subject; let’s hear about it from an informed source!

Posted by: Marty Tysanner on July 14, 2005 3:51 AM | Permalink | Reply to this

### Re: Panel discussion

I didn’t attend the conference, but have the impression that the panel discussion was relevant to making an informed decision about risks of studying string theory.

The topic of the Panel discussion was “The Next String Revolution.” If you think that a bunch of people prognosticating about future “revolutions” in their field is of the slightest relevance to anything, then I have a bridge you might be interested in buying …

… making an informed decision about risks of studying string theory.

A formulation of the question that only a reader of Peter Woit’s blog would come up with.

Lookit, if you’re trying to decide what to work on, you want to see what progress people are making in the field now, not what progress they think they will be making 10 years from now.

Lots of interesting talks at this conference (I wish I had the energy to blog about more than a handful). Lots of interesting things going on in the field. I don’t get the sense that people feel “stuck,” or are thrashing about for stuff to do.

As a graduate student, you need to find something to work on now, not 10 years from now. So these prognostications — even if they were accurate, which they surely are not — are irrelevant to you.

The other thing you need to do as a graduate student is get trained as broadly as possible. I didn’t mention the survey talks on LHC physics (Friday) and Cosmology (Monday), but there is real data coming in and much more to start coming soon to our field; you need to be prepared to think about it.

The most intelligent thing said at the panel discussion was when Martin Rocek (in a question from the audience) suggested that people should be thinking about neutrino masses. They’re being observed now, and they’re a window into very high energy ($M_{\text{new}}\sim 10^{15}$ GeV) physics.

I, personally, would much rather think about that, rather than about when the next Revolution is coming.

Posted by: Jacques Distler on July 14, 2005 7:39 AM | Permalink | PGP Sig | Reply to this

### Re: If It’s Tuesday, This Must Be Toronto

Congratulations on your new paper. I have to admit I didn’t think you were a landscapist. My admiration for some of your work must have tricked me into thinking that you would not go along with that fashionable anthropic BS…

Best wishes,
Dan

Posted by: Dan on July 12, 2005 9:27 PM | Permalink | Reply to this

### Congratulations or condolences?

I have to admit I didn’t think you were a landscapist.

I hope you read beyond the abstract before deciding that I’ve gone over to the Dark Side.

… that you would not go along with that fashionable …

I never do anything because it’s “fashionable.”

Posted by: Jacques Distler on July 12, 2005 11:09 PM | Permalink | PGP Sig | Reply to this

### Re: If It’s Tuesday, This Must Be Toronto

I never do anything because it’s “fashionable.”

I see, not even blogging ;-) ?

Posted by: big fish on July 13, 2005 1:32 AM | Permalink | Reply to this

### Slave of fashion

Touché!  :-)

(Though, in my defence, no one in late 2002 when I started this blog, had thought to try to use this medium for serious physics discussions. And it’s still not exactly a “fashionable” idea.)

Posted by: Jacques Distler on July 13, 2005 6:46 AM | Permalink | PGP Sig | Reply to this

### Re: Slave of fashion

… and now in 2005, I am not sure if we can count more than one handful of blogs trying to do it.

Posted by: Alejandro Rivero on July 13, 2005 11:31 AM | Permalink | Reply to this
Read the post Panel Discussion in Toronto
Weblog: Not Even Wrong
Excerpt: Last night there was a panel discussion on "The Next Superstring Revolution" at Strings 2005 in Toronto. I'm curious about what took place there, so wondering if anyone who attended can tell us what happened, or at least whether it...
Tracked: July 13, 2005 10:10 AM

### Re: If It’s Tuesday, This Must Be Toronto

“I hope you read beyond the abstract before deciding that I’ve gone over to the Dark Side.”

I am sure you have a good point, and I promise not to judge before I understand it. But I *have* read beyond the abstract and it still – superficially – looks like the Dark Side is not too far. Can you please explain what saves the day (and your reputation)?

Thanks,
Dan

Posted by: Dan on July 13, 2005 2:23 PM | Permalink | Reply to this

### Technological Determinism

For reasons that I hope I do not have to explain, I think it is rather important to understand effective field theories with a large number of “moduli” (whose degeneracy is lifted at a scale $M_c\ll M_p$).

What we’ve done is build a machine which is useful for studying the properties of such theories. When I gave a seminar about this at Harvard, Cumrun (after my talk) had a reaction similar to yours,

Yes, yes, Jacques. It’s a beautiful machine. But, you know, good machines can be put to bad purposes.

I happen not to be a technological determinist.

Beside which, if you read far enough, you might even see where we explain how our results might actually kill the “friendly landscape” idea. I don’t know whether they do or don’t, but one would never even be able to address the question if we hadn’t done our work.

Posted by: Jacques Distler on July 13, 2005 3:36 PM | Permalink | PGP Sig | Reply to this

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